1. Field of the Invention
The present invention relates to a method of storing a dry image-forming material using light-sensitive microcapsules, specifically to a method of storing a dry image-forming material which has an excellent storage stability during production and use.
2. Description of Prior Art
Imaging processes based on photosensitive microencapsulated materials are well known. The Meed Corporation discloses a method for forming an image through exposure-controlled release of an image-forming agent from a microcapsule containing a photohardenable composition in U.S. Pat. Nos. 4,399,209, 4,440,846 and 4,772,541.
In the method, a colorless image-forming agent, called a leuco dye, which is released under exposure-control from a microcapsule, is reacted with a color-developer present outside the microcapsule to form a color image.
U.S. Pat. No. 4,399,209 describes a transfer imaging system. That is, an image-forming agent is image-wise transferred to a developer sheet containing a chromogenic material and reacted with a developer to form an image. U.S. Pat. No. 4,440,846 discloses a `self-contained` system wherein an imaging system and a developer are present on the same support. That is, an image-forming agent is encapsulated in pressure-rupturable capsules, and upon exposure and capsule rupture the image-forming agent contacts and reacts with the developer to form an image on the support. These methods have excellent characteristics as a dry color imaging method.
The above imaging material cures the internal phase of a microcapsule or increases the viscosity thereof to control the release of a color precursor in pressure-rupturing to form a positive-positive image pattern upon exposure to light. However, it has the defect that the degree of hardening of the internal phase of a microcapsule or increasing the viscosity thereof is varied by a change in environment, particularly a variation in humidity, and as a result thereof, photographic characteristics such as light-sensitivity, maximum density and fogging density are changed.
This defect presents a serious problem in full color imaging. That is, in forming a full color image, color precursors which develop into yellow, magenta and cyan colors and photo-initiators corresponding to blue, green and red lights are encapsulated in an internal phase of the microcapsules, and the three sets of the microcapsules are mixed to prepare a full color imaging material containing a developer. However, the photographic characteristics of the respective microcapsules vary with a change in humidity to different degrees, which results in causing a problem of producing muddy colors.
That is, for example, when a yellow color is developed, cyan and magenta capsules are cured by red and green lights, and only a yellow color former reacts with a color-developer to form an image. However, the cyan or magenta capsule may insufficiently cure due to a change in humidity in certain cases, and as a result thereof, a muddy color in which cyan or magenta is blended with yellow is produced in some cases.
Such a muddy color phenomenon due to a change in humidity has been a large problem in designing a processor for forming an image when an imaging material is used as a system material to be integrated with hardware, particularly in the case when an imaging material is used as an output material for an image on a personal computer.